X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperltodo.pod;h=a16cf0d604adff14905f09dfc0f43ed39d2aacd2;hb=e706c0cd31a70bd2c97d4510f261613278a7e1f5;hp=09ed1ff1e23d4f2ef846373bb5f51423b14cb561;hpb=c4aca7d03737ddcac23de1ad6d597e98be679214;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perltodo.pod b/pod/perltodo.pod index 09ed1ff..a16cf0d 100644 --- a/pod/perltodo.pod +++ b/pod/perltodo.pod @@ -4,84 +4,786 @@ perltodo - Perl TO-DO List =head1 DESCRIPTION -This is a list of wishes for Perl. Send updates to -I. If you want to work on any of these -projects, be sure to check the perl5-porters archives for past ideas, -flames, and propaganda. This will save you time and also prevent you -from implementing something that Larry has already vetoed. One set -of archives may be found at: +This is a list of wishes for Perl. The most up to date version of this file +is at http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod + +The tasks we think are smaller or easier are listed first. Anyone is welcome +to work on any of these, but it's a good idea to first contact +I to avoid duplication of effort, and to learn from +any previous attempts. By all means contact a pumpking privately first if you +prefer. + +Whilst patches to make the list shorter are most welcome, ideas to add to +the list are also encouraged. Check the perl5-porters archives for past +ideas, and any discussion about them. One set of archives may be found at: http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ -=head1 assertions +What can we offer you in return? Fame, fortune, and everlasting glory? Maybe +not, but if your patch is incorporated, then we'll add your name to the +F file, which ships in the official distribution. How many other +programming languages offer you 1 line of immortality? -Clean up and finish support for assertions. See L. +=head1 Tasks that only need Perl knowledge -=head1 iCOW +=head2 Improve Porting/cmpVERSION.pl to work from git tags -Sarathy and Arthur have a proposal for an improved Copy On Write which -specifically will be able to COW new ithreads. If this can be implemented -it would be a good thing. +See F for a bit more detail. -=head1 (?{...}) closures in regexps +=head2 Migrate t/ from custom TAP generation -Fix (or rewrite) the implementation of the C closures. +Many tests below F still generate TAP by "hand", rather than using library +functions. As explained in L, tests in F are +written in a particular way to test that more complex constructions actually +work before using them routinely. Hence they don't use C, but +instead there is an intentionally simpler library, F. However, +quite a few tests in F have not been refactored to use it. Refactoring +any of these tests, one at a time, is a useful thing TODO. -=head1 A re-entrant regexp engine +The subdirectories F, F and F, that contain the most +basic tests, should be excluded from this task. -This will allow the use of a regex from inside (?{ }), (??{ }) and -(?(?{ })|) constructs. +=head2 Test that regen.pl was run -=head1 pragmata +There are various generated files shipped with the perl distribution, for +things like header files generate from data. The generation scripts are +written in perl, and all can be run by F. However, because they're +written in perl, we can't run them before we've built perl. We can't run them +as part of the F, because changing files underneath F confuses +it completely, and we don't want to run them automatically anyway, as they +change files shipped by the distribution, something we seek not do to. -=head2 lexical pragmas +If someone changes the data, but forgets to re-run F then the +generated files are out of sync. It would be good to have a test in +F that checks that the generated files are in sync, and fails +otherwise, to alert someone before they make a poor commit. I suspect that this +would require adapting the scripts run from F to have dry-run +options, and invoking them with these, or by refactoring them into a library +that does the generation, which can be called by the scripts, and by the test. -Reimplement the mechanism of lexical pragmas to be more extensible. Fix -current pragmas that don't work well (or at all) with lexical scopes or in -run-time eval(STRING) (C, C, C for example). MJD has a -preliminary patch that implements this. +=head2 Automate perldelta generation -=head2 use less 'memory' +The perldelta file accompanying each release summaries the major changes. +It's mostly manually generated currently, but some of that could be +automated with a bit of perl, specifically the generation of -Investigate trade offs to switch out perl's choices on memory usage. -Particularly perl should be able to give memory back. +=over + +=item Modules and Pragmata + +=item New Documentation + +=item New Tests + +=back + +See F for details. + +=head2 Remove duplication of test setup. + +Schwern notes, that there's duplication of code - lots and lots of tests have +some variation on the big block of C<$Is_Foo> checks. We can safely put this +into a file, change it to build an C<%Is> hash and require it. Maybe just put +it into F. Throw in the handy tainting subroutines. + +=head2 POD -E HTML conversion in the core still sucks + +Which is crazy given just how simple POD purports to be, and how simple HTML +can be. It's not actually I simple as it sounds, particularly with the +flexibility POD allows for C<=item>, but it would be good to improve the +visual appeal of the HTML generated, and to avoid it having any validation +errors. See also L, as the layout of installation tree +is needed to improve the cross-linking. + +The addition of C and its related modules may make this task +easier to complete. + +=head2 Make ExtUtils::ParseXS use strict; + +F contains this line + + # use strict; # One of these days... + +Simply uncomment it, and fix all the resulting issues :-) + +The more practical approach, to break the task down into manageable chunks, is +to work your way though the code from bottom to top, or if necessary adding +extra C<{ ... }> blocks, and turning on strict within them. + +=head2 Make Schwern poorer + +We should have tests for everything. When all the core's modules are tested, +Schwern has promised to donate to $500 to TPF. We may need volunteers to +hold him upside down and shake vigorously in order to actually extract the +cash. + +=head2 Improve the coverage of the core tests + +Use Devel::Cover to ascertain the core modules' test coverage, then add +tests that are currently missing. + +=head2 test B + +A full test suite for the B module would be nice. + +=head2 A decent benchmark + +C seems impervious to any recent changes made to the perl core. It +would be useful to have a reasonable general benchmarking suite that roughly +represented what current perl programs do, and measurably reported whether +tweaks to the core improve, degrade or don't really affect performance, to +guide people attempting to optimise the guts of perl. Gisle would welcome +new tests for perlbench. + +=head2 fix tainting bugs + +Fix the bugs revealed by running the test suite with the C<-t> switch (via +C). + +=head2 Dual life everything + +As part of the "dists" plan, anything that doesn't belong in the smallest perl +distribution needs to be dual lifed. Anything else can be too. Figure out what +changes would be needed to package that module and its tests up for CPAN, and +do so. Test it with older perl releases, and fix the problems you find. + +To make a minimal perl distribution, it's useful to look at +F. + +=head2 Move dual-life pod/*.PL into ext + +Nearly all the dual-life modules have been moved to F. However, we +still need to move F into their respective directories +in F. They're referenced by (at least) C in F +and C in F and F, and listed +explicitly in F, F and F + +=head2 POSIX memory footprint + +Ilya observed that use POSIX; eats memory like there's no tomorrow, and at +various times worked to cut it down. There is probably still fat to cut out - +for example POSIX passes Exporter some very memory hungry data structures. + +=head2 embed.pl/makedef.pl + +There is a script F that generates several header files to prefix +all of Perl's symbols in a consistent way, to provide some semblance of +namespace support in C. Functions are declared in F, variables +in F. Quite a few of the functions and variables +are conditionally declared there, using C<#ifdef>. However, F +doesn't understand the C macros, so the rules about which symbols are present +when is duplicated in F. Writing things twice is bad, m'kay. +It would be good to teach C to understand the conditional +compilation, and hence remove the duplication, and the mistakes it has caused. + +=head2 use strict; and AutoLoad + +Currently if you write + + package Whack; + use AutoLoader 'AUTOLOAD'; + use strict; + 1; + __END__ + sub bloop { + print join (' ', No, strict, here), "!\n"; + } + +then C isn't in force within the autoloaded subroutines. It would +be more consistent (and less surprising) to arrange for all lexical pragmas +in force at the __END__ block to be in force within each autoloaded subroutine. + +There's a similar problem with SelfLoader. + +=head2 profile installman + +The F script is slow. All it is doing text processing, which we're +told is something Perl is good at. So it would be nice to know what it is doing +that is taking so much CPU, and where possible address it. + +=head2 enable lexical enabling/disabling of inidvidual warnings + +Currently, warnings can only be enabled or disabled by category. There +are times when it would be useful to quash a single warning, not a +whole category. + +=head1 Tasks that need a little sysadmin-type knowledge + +Or if you prefer, tasks that you would learn from, and broaden your skills +base... + +=head2 make HTML install work + +There is an C target in the Makefile. It's marked as +"experimental". It would be good to get this tested, make it work reliably, and +remove the "experimental" tag. This would include + +=over 4 + +=item 1 + +Checking that cross linking between various parts of the documentation works. +In particular that links work between the modules (files with POD in F) +and the core documentation (files in F) + +=item 2 + +Work out how to split C into chunks, preferably one per function +group, preferably with general case code that could be used elsewhere. +Challenges here are correctly identifying the groups of functions that go +together, and making the right named external cross-links point to the right +page. Things to be aware of are C<-X>, groups such as C to +C, two or more C<=items> giving the different parameter lists, such +as + + =item substr EXPR,OFFSET,LENGTH,REPLACEMENT + =item substr EXPR,OFFSET,LENGTH + =item substr EXPR,OFFSET + +and different parameter lists having different meanings. (eg C) +=head2 UTF-8 revamp -=back +The handling of Unicode is unclean in many places. For example, the regexp +engine matches in Unicode semantics whenever the string or the pattern is +flagged as UTF-8, but that should not be dependent on an internal storage +detail of the string. -=head2 put patchlevel in -v +=head2 Properly Unicode safe tokeniser and pads. -Currently perl from p4/rsync ships with a patchlevel.h file that usually -defines one local patch, of the form "MAINT12345" or "RC1". The output of -perl -v doesn't report that a perl isn't an official release, and this -information can get lost in bugs reports. Because of this, the minor version -isn't bumped up until RC time, to minimise the possibility of versions of perl -escaping that believe themselves to be newer than they actually are. +The tokeniser isn't actually very UTF-8 clean. C is a hack - +variable names are stored in stashes as raw bytes, without the utf-8 flag +set. The pad API only takes a C pointer, so that's all bytes too. The +tokeniser ignores the UTF-8-ness of C, or any SVs returned from +source filters. All this could be fixed. -It would be useful to find an elegant way to have the "this is an interim -maintenance release" or "this is a release candidate" in the terse -v output, -and have it so that it's easy for the pumpking to remove this just as the -release tarball is rolled up. This way the version pulled out of rsync would -always say "I'm a development release" and it would be safe to bump the -reported minor version as soon as a release ships, which would aid perl -developers. +=head2 state variable initialization in list context -=head1 Incremental things +Currently this is illegal: -Some tasks that don't need to get done in one big hit. + state ($a, $b) = foo(); -=head2 autovivification +In Perl 6, C and C<(state $a) = foo();> have different +semantics, which is tricky to implement in Perl 5 as currently they produce +the same opcode trees. The Perl 6 design is firm, so it would be good to +implement the necessary code in Perl 5. There are comments in +C that show the code paths taken by various assignment +constructions involving state variables. -Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict; +=head2 Implement $value ~~ 0 .. $range -=head2 fix tainting bugs +It would be nice to extend the syntax of the C<~~> operator to also +understand numeric (and maybe alphanumeric) ranges. -Fix the bugs revealed by running the test suite with the C<-t> switch (via -C). +=head2 A does() built-in -=head2 Make tainting consistent +Like ref(), only useful. It would call the C method on objects; it +would also tell whether something can be dereferenced as an +array/hash/etc., or used as a regexp, etc. +L -Tainting would be easier to use if it didn't take documented shortcuts and allow -taint to "leak" everywhere within an expression. +=head2 Tied filehandles and write() don't mix -=head2 Dual life everything +There is no method on tied filehandles to allow them to be called back by +formats. -As part of the "dists" plan, anything that doesn't belong in the smallest perl -distribution needs to be dual lifed. Anything else can be too. +=head2 Propagate compilation hints to the debugger -=head1 Vague things +Currently a debugger started with -dE on the command-line doesn't see the +features enabled by -E. More generally hints (C<$^H> and C<%^H>) aren't +propagated to the debugger. Probably it would be a good thing to propagate +hints from the innermost non-C scope: this would make code eval'ed +in the debugger see the features (and strictures, etc.) currently in +scope. -Some more nebulous ideas +=head2 Attach/detach debugger from running program -=head2 threads +The old perltodo notes "With C, you can attach the debugger to a running +program if you pass the process ID. It would be good to do this with the Perl +debugger on a running Perl program, although I'm not sure how it would be +done." ssh and screen do this with named pipes in /tmp. Maybe we can too. -=over 4 +=head2 LVALUE functions for lists -=item * +The old perltodo notes that lvalue functions don't work for list or hash +slices. This would be good to fix. -Re-implement C<:unique> in a way that is actualy thread-safe +=head2 regexp optimiser optional -=item * +The regexp optimiser is not optional. It should configurable to be, to allow +its performance to be measured, and its bugs to be easily demonstrated. -Make C share aggregates properly +=head2 delete &function -(these two may actually share approach, if not implementation +Allow to delete functions. One can already undef them, but they're still +in the stash. -=back +=head2 C regex modifier -Generally make threads more robust. See also L +That flag would enable to match whole words, and also to interpolate +arrays as alternations. With it, C

would be roughly equivalent to: -=head2 POSIX memory footprint + do { local $"='|'; /\b(?:P)\b/ } -Ilya observed that use POSIX; eats memory like there's no tomorrow, and at -various times worked to cut it down. There is probably still fat to cut out - -for example POSIX passes Exporter some very memory hungry data structures. +See L +for the discussion. + +=head2 optional optimizer + +Make the peephole optimizer optional. Currently it performs two tasks as +it walks the optree - genuine peephole optimisations, and necessary fixups of +ops. It would be good to find an efficient way to switch out the +optimisations whilst keeping the fixups. + +=head2 You WANT *how* many + +Currently contexts are void, scalar and list. split has a special mechanism in +place to pass in the number of return values wanted. It would be useful to +have a general mechanism for this, backwards compatible and little speed hit. +This would allow proposals such as short circuiting sort to be implemented +as a module on CPAN. + +=head2 lexical aliases + +Allow lexical aliases (maybe via the syntax C. + +=head2 entersub XS vs Perl + +At the moment pp_entersub is huge, and has code to deal with entering both +perl and XS subroutines. Subroutine implementations rarely change between +perl and XS at run time, so investigate using 2 ops to enter subs (one for +XS, one for perl) and swap between if a sub is redefined. + +=head2 Self-ties + +Self-ties are currently illegal because they caused too many segfaults. Maybe +the causes of these could be tracked down and self-ties on all types +reinstated. =head2 Optimize away @_ The old perltodo notes "Look at the "reification" code in C". -=head2 switch ops +=head2 Virtualize operating system access + +Implement a set of "vtables" that virtualizes operating system access +(open(), mkdir(), unlink(), readdir(), getenv(), etc.) At the very +least these interfaces should take SVs as "name" arguments instead of +bare char pointers; probably the most flexible and extensible way +would be for the Perl-facing interfaces to accept HVs. The system +needs to be per-operating-system and per-file-system +hookable/filterable, preferably both from XS and Perl level +(L is good reading at this point, +in fact, all of L is.) + +This has actually already been implemented (but only for Win32), +take a look at F and F. While all Win32 +variants go through a set of "vtables" for operating system access, +non-Win32 systems currently go straight for the POSIX/Unix-style +system/library call. Similar system as for Win32 should be +implemented for all platforms. The existing Win32 implementation +probably does not need to survive alongside this proposed new +implementation, the approaches could be merged. + +What would this give us? One often-asked-for feature this would +enable is using Unicode for filenames, and other "names" like %ENV, +usernames, hostnames, and so forth. +(See L.) + +But this kind of virtualization would also allow for things like +virtual filesystems, virtual networks, and "sandboxes" (though as long +as dynamic loading of random object code is allowed, not very safe +sandboxes since external code of course know not of Perl's vtables). +An example of a smaller "sandbox" is that this feature can be used to +implement per-thread working directories: Win32 already does this. + +See also L. + +=head2 Investigate PADTMP hash pessimisation + +The peephole optimiser converts constants used for hash key lookups to shared +hash key scalars. Under ithreads, something is undoing this work. +See http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html + +=head2 Store the current pad in the OP slab allocator + +=for clarification +I hope that I got that "current pad" part correct + +Currently we leak ops in various cases of parse failure. I suggested that we +could solve this by always using the op slab allocator, and walking it to +free ops. Dave comments that as some ops are already freed during optree +creation one would have to mark which ops are freed, and not double free them +when walking the slab. He notes that one problem with this is that for some ops +you have to know which pad was current at the time of allocation, which does +change. I suggested storing a pointer to the current pad in the memory allocated +for the slab, and swapping to a new slab each time the pad changes. Dave thinks +that this would work. + +=head2 repack the optree + +Repacking the optree after execution order is determined could allow +removal of NULL ops, and optimal ordering of OPs with respect to cache-line +filling. The slab allocator could be reused for this purpose. I think that +the best way to do this is to make it an optional step just before the +completed optree is attached to anything else, and to use the slab allocator +unchanged, so that freeing ops is identical whether or not this step runs. +Note that the slab allocator allocates ops downwards in memory, so one would +have to actually "allocate" the ops in reverse-execution order to get them +contiguous in memory in execution order. + +See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html + +Note that running this copy, and then freeing all the old location ops would +cause their slabs to be freed, which would eliminate possible memory wastage if +the previous suggestion is implemented, and we swap slabs more frequently. + +=head2 eliminate incorrect line numbers in warnings + +This code + + use warnings; + my $undef; + + if ($undef == 3) { + } elsif ($undef == 0) { + } + +used to produce this output: -The old perltodo notes "Although we have C in core, Larry points to -the dormant C and C ops in F; using these opcodes would -be much faster." + Use of uninitialized value in numeric eq (==) at wrong.pl line 4. + Use of uninitialized value in numeric eq (==) at wrong.pl line 4. -=head2 Attach/detach debugger from running program +where the line of the second warning was misreported - it should be line 5. +Rafael fixed this - the problem arose because there was no nextstate OP +between the execution of the C and the C, hence C still +reports that the currently executing line is line 4. The solution was to inject +a nextstate OPs for each C, although it turned out that the nextstate +OP needed to be a nulled OP, rather than a live nextstate OP, else other line +numbers became misreported. (Jenga!) -The old perltodo notes "With C, you can attach the debugger to a running -program if you pass the process ID. It would be good to do this with the Perl -debugger on a running Perl program, although I'm not sure how it would be done." -ssh and screen do this with named pipes in tmp. Maybe we can too. +The problem is more general than C (although the C case is the +most common and the most confusing). Ideally this code -=head2 A decent benchmark + use warnings; + my $undef; + + my $a = $undef + 1; + my $b + = $undef + + 1; -perlbench seems impervious to any recent changes made to the perl core. It would -be useful to have a reasonable general benchmarking suite that roughly -represented what current perl programs do, and measurably reported whether -tweaks to the core improve, degrade or don't really affect performance, to -guide people attempting to optimise the guts of perl. +would produce this output -=head2 readpipe(LIST) + Use of uninitialized value $undef in addition (+) at wrong.pl line 4. + Use of uninitialized value $undef in addition (+) at wrong.pl line 7. -system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid -running a shell. readpipe() (the function behind qx//) could be similarly -extended. +(rather than lines 4 and 5), but this would seem to require every OP to carry +(at least) line number information. + +What might work is to have an optional line number in memory just before the +BASEOP structure, with a flag bit in the op to say whether it's present. +Initially during compile every OP would carry its line number. Then add a late +pass to the optimiser (potentially combined with L) which +looks at the two ops on every edge of the graph of the execution path. If +the line number changes, flags the destination OP with this information. +Once all paths are traced, replace every op with the flag with a +nextstate-light op (that just updates C), which in turn then passes +control on to the true op. All ops would then be replaced by variants that +do not store the line number. (Which, logically, why it would work best in +conjunction with L, as that is already copying/reallocating +all the OPs) + +(Although I should note that we're not certain that doing this for the general +case is worth it) + +=head2 optimize tail-calls + +Tail-calls present an opportunity for broadly applicable optimization; +anywhere that C<< return foo(...) >> is called, the outer return can +be replaced by a goto, and foo will return directly to the outer +caller, saving (conservatively) 25% of perl's call&return cost, which +is relatively higher than in C. The scheme language is known to do +this heavily. B::Concise provides good insight into where this +optimization is possible, ie anywhere entersub,leavesub op-sequence +occurs. + + perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)' + +Bottom line on this is probably a new pp_tailcall function which +combines the code in pp_entersub, pp_leavesub. This should probably +be done 1st in XS, and using B::Generate to patch the new OP into the +optrees. + +=head1 Big projects + +Tasks that will get your name mentioned in the description of the "Highlights +of 5.12" + +=head2 make ithreads more robust + +Generally make ithreads more robust. See also L + +This task is incremental - even a little bit of work on it will help, and +will be greatly appreciated. + +One bit would be to write the missing code in sv.c:Perl_dirp_dup. + +Fix Perl_sv_dup, et al so that threads can return objects. + +=head2 iCOW + +Sarathy and Arthur have a proposal for an improved Copy On Write which +specifically will be able to COW new ithreads. If this can be implemented +it would be a good thing. + +=head2 (?{...}) closures in regexps + +Fix (or rewrite) the implementation of the C closures. + +=head2 A re-entrant regexp engine + +This will allow the use of a regex from inside (?{ }), (??{ }) and +(?(?{ })|) constructs. + +=head2 Add class set operations to regexp engine + +Apparently these are quite useful. Anyway, Jeffery Friedl wants them. + +demerphq has this on his todo list, but right at the bottom. + + +=head1 Tasks for microperl + + +[ Each and every one of these may be obsolete, but they were listed + in the old Todo.micro file] + + +=head2 make creating uconfig.sh automatic + +=head2 make creating Makefile.micro automatic + +=head2 do away with fork/exec/wait? + +(system, popen should be enough?) + +=head2 some of the uconfig.sh really needs to be probed (using cc) in buildtime: -=head2 Self ties +(uConfigure? :-) native datatype widths and endianness come to mind -self ties are currently illegal because they caused too many segfaults. Maybe -the causes of these could be tracked down and self-ties on all types re- -instated.